The thing about eating more than you'd like to when you've had a life-long problem with overeating is that you can be filled with fear that you're perched on a sled at the top of a snowy mountain and that one day of eating more than necessary will be the tap that sends you sliding down. I've found that this sense of losing control is rapidly mitigated by just one day of getting back on your plan. It really doesn't take much success to help you feel that failure isn't going to become the norm.
This experience has taught me that one further emotional aspect to this which I need to work on is the sense that any lapse in control is the start of a "permanent" loss of control. It's not that such a fear is unfounded. If you've tried to get a handle on your eating and failed enough times, you've got a sound basis in personal history for doubting yourself. That being said, I have to realize that I am not the person who failed before. I'm the person who is succeeding now, and this person has chosen a path which was paved more solidly than the one who failed before.